48V Battery

[flecc]

How about voltage? I have seen somewhere that 48V is the limit. Would that make 48V batteries illegal (as they can be charged above 48V)? Or 48V limit is set on battery nominal voltage?

It's 50 volts, so technically a fully charge battery will exceed that. That is why some companies use an in between voltage, 43 volts in Wisper's case.

But I think its worrying about nothing. The moment an EAPC comes under load the overvolts will disappear, returning when slacking off, so the mean voltage even when fully charged will be OK. The police have better things to do than organise dynamic testing of EAPC battery voltages and the couple of times they've tried similar they've come unstuck through inadequate knowledge.
.

 

[saneagle]

Bikes with 48v batteries (13S) have been certified as complying with EN15194, so they are allowed and legal. In the UK, there is no specific law that specifies a voltage limit. If you look at the info on the government site, there's no mention of voltage.

 

[Voltsnamps]

The law doesn't limit capacity, only the weight your bike can comfortably carry and your wallet do that.
.

I don’t think any of the keyboard lawyers would argue with that,
My point was only that (Samsung) 21700 cells give you more w/hr per gram than 18650’s. Yes, wallet call but no going back once you know. Changed the game for me, my latest battery cost 75% of a complete Aldi ebike but takes me where I want to go. The other 25% spent on s/h cycles and a bit added for motor.
One big fkr weighs an awful lot less than 2 of Op’s and goes 3x as far, what was the question ?

 

[harrys]

Google says 21700's are 300WH/kg while 18650's are 250W/kg. However, I see my Samsung 50E's are said to be 68-70 grams, while my 18650 GA's are 45-48 grams. Using the max capacity of 5WH and 3.5WH respectively, I'm calculating 260-280 WH/kg for both type of cells, no real advantage in weight,

However, I have been able to get both cell sizes for the same price, so there is a big cost advantage for 21700.

 

[Nealh]

For me 18650 is still king for my small 44v bottle battery builds , one simply can't do it with 21700 format. Otherwise 21700 format is the one for general battery builds or the nice 18650 Sam 35e3 or Moli's.

Molicell is the chosen cell selected by UK venture EVTL / Vertical aerospace for their EV vtol aircraft , hoping they make the grade as have some £££'s riding on their success. Hopefully they get their #2 a/c flying for Farnboro and the share price can rise.

 

[Peter.Bridge]

For me 18650 is still king for my small 44v bottle battery builds , one simply can't do it with 21700 format. Otherwise 21700 format is the one for general battery builds or the nice 18650 Sam 35e3 or Moli's.

Molicell is the chosen cell selected by UK venture EVTL / Vertical aerospace for their EV vtol aircraft , hoping they make the grade as have some £££'s riding on their success. Hopefully they get their #2 a/c flying for Farnboro and the share price can rise.

Is there any difference in capacity between the different cells ? I was wondering what the lightest possible battery would be for a given capacity - although I think the casing is a significant component of the weight

 

[Nealh]

Capacity varies a lot.
Typically 18650 is approx. 3450mah for a 3500mah rated cell, where as a 21700 cell is 4200mah - 5000mah .
My small ali bottle battery with 24 LG hg2 's is 44v/6000mah and weighs in at 1.436kg.
My 21700 moli with 24 P42's is 44v/8400mah weighs in at 2.209kg.

Indeed it is the casing that can add a bit of weight.

My bottle battery is a Ali drinks bottle so lightest likely one can find giving good protection.
My P42 pack is a simple flat oblong shape in a soft padded case, for protection inside it is encased with the light thin hobby fibreglass board one can buy.

Both cells are higher discharge rated to enable decent performance with only a 2p build and low voltage sag.

 

[Voltsnamps]

Capacity varies a lot.
Typically 18650 is approx. 3450mah for a 3500mah rated cell, where as a 21700 cell is 4200mah - 5000mah .
My small ali bottle battery with 24 LG hg2 's is 44v/6000mah and weighs in at 1.436kg.
My 21700 moli with 24 P42's is 44v/8400mah weighs in at 2.209kg.

Indeed it is the casing that can add a bit of weight.

My bottle battery is a Ali drinks bottle so lightest likely one can find giving good protection.
My P42 pack is a simple flat oblong shape in a soft padded case, for protection inside it is encased with the light thin hobby fibreglass board one can buy.

Both cells are higher discharge rated to enable decent performance with only a 2p build and low voltage sag.

Absolutely how I work, 6/1.436
Or 8.4/2.209
what was the question ?
3500 18650’s have their place, but dear
50E 21700 if space allows

 

[Peter.Bridge]

what was the question ?

My question really was if I wanted a 48V nominal battery, capacity say 17Ah , with a max discharge rate of 30A, is there a noticeable weight difference depending on the type or brand of cells used

 

[saneagle]

My question really was if I wanted a 48V nominal battery, capacity say 17Ah , with a max discharge rate of 30A, is there a noticeable weight difference depending on the type or brand of cells used

Not on the brand of cells, but there would be if different versions of the cells were used. Some cells have higher capacity than others. Generally high capacity cells don't give as much current as low capacity ones. 17ah can be achieved with 65 x 3.35 ah 18650 cells. 30amps would be OK as long as you don't want it continuously.

Most 2170 cells are 5ah, so 52 would give 20ah, or 39 would give 15ah.

In other words if you want 48v 17ah, there's only one choice, and if you need 30 amps continuous, it would probably be better to go down to 2.5ah cells, which would only be 12.5ah for a 65 cell battery. A 78 cell one would give you 15ah, but would be too heavy.

 

[harrys]

My question really was if I wanted a 48V nominal battery, capacity say 17Ah , with a max discharge rate of 30A, is there a noticeable weight difference depending on the type or brand of cells used

Here's some possibilities.

Make	Cell	Capacity	Weight	Packing	AH	Weight
Sanyo	GA	3.5Ah	45 g	13S-5P	48V17.5​	2925​
Molicell	P42A	4.2Ah	70 g	13S-4P	48V16.8​	3640​
Sanyo	50E	5.0Ah	70g	13S-3P	48V15.0​	2730​

The above is cell weights only. You'll have to see what your case and BMS weighs, plus the wiring, etc. You can cut down to 2340 grams of cells if you did a 48V14Ah pack a 13S-4P array of GA's.

 

[harrys]

For a small motor. like the TSDZ2 in Eco/Tour mode, does a 14S-1P battery made with Molicel P42A's make sense? My TSDZ2 only pulls 8A max riding around with light assist, and peaks at 12A in turbo, according to my wattmeter.

Looking at the discharge curves, the P42A will do at least 3.5AH at a constant 10A draw, so it might hold up OK in a 1P string.

I could always make a 13S-2P in 21700, but I've done it and it's not small at all in a bottle configuration. The 18650 Sanyo GA in a 13S-2P makes for a nice bottle battery,

 

[Az.]

My question really was if I wanted a 48V nominal battery, capacity say 17Ah , with a max discharge rate of 30A, is there a noticeable weight difference depending on the type or brand of cells used

I asked myself the same question and I find it purely academical. In practice you will find a very few batteries available on the market. I don't see any major differences between batteries with 18650 and 21700 cells. After all they use the same technology and the only difference is size of the cell.

Size of battery pack with 18650 cells and battery pack with 2170 cells is usually the same, so at the end of the day all comes down to price. Just make sure cells are good and you can't go wrong.